Recently, further improvement in durability of tires is being required based on the social requirement for the material saving, and a rubber composition exhibiting a greater resistance to cut growth is desired. However, a softener is necessary for a rubber composition for tire sidewall so that the sufficient workability is maintained, and improving the resistance to cut growth without adversely affecting workability has been difficult when a softener is present.
Improvements in the rubber component have been attempted to overcome the above problem. For example, in Patent Reference 1, it is proposed that the resistance to cut growth is improved by disposing a specific ethylene-propylene-diene terpolymer at tire sidewall.
In Patent Reference 2, it is proposed that contents of the cis-1,4-bond and the vinyl bond in polybutadiene rubber obtained by polymerization in the presence of a catalyst having a specific rare earth element are limited to specific ranges to improve the resistance to cut growth.
However, it remains difficult that the excellent resistance to cut growth is obtained while the sufficient workability is exhibited, and it is desired that the excellent resistance to cut growth is obtained while the sufficient workability is surely exhibited
[Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei 8 (1996)-20202
[Patent Reference 2] Japanese Patent Application Laid-Open No. 2005-15590